This problem is a classic when it comes to advanced routing / VPN.
The solution would be to define a static route (active, private) with your public IP as destination, give it a C-Class subnet, set it to interface "LAN" and give it the metric 1 (or 0).
The problem is that the GUI of this router only allows a metric from 2-15, so the router itself has higher priority and your rule will never work.
The scenario you want is called hairpinning.
Unfortunately this router seems not to offer CLI where you would be free to configure what you need.
If you have another IP at your disposal there would be the solution of 1:1 NAT but it looks that this router only supports 1:1 NAT xor NAT with one shared WAN address.
Routing instead of NAT is of course also an option but if you want to supply internet access to a lot of clients, which I think is the case because you bought a wireless router, you are in a n unlucky situation.
FYI am currently dealing with the exact same problem.
Here is a thread on cisco forums that corresponds to the problem. I didnt yet read all through it but there seems to be BETA firmware available that resolves the issue.
There is a Beta Firmware which will
resolve the issue. You must call the
Small Business Support Center to get
it (1-866-606-1866). Simply call, open
a ticket, and tell the agent you're
seeking RV120W Beta Firmware.
If you find a solution or get the firmware and it works for me please let me know by commenting on this answer. I will do the same :)
Also this question might be worth migrating to ServerFault.
Also I must add that I am not an expert at this subject, I am not 100% positive that I say is true, but I am very confident its correct. Another opinion would be nice. please feel free to comment on this answer if anything is wrong so i can adapt it.
I just hang in with the cisco support. The problem is known and documented. I am currently having an issue signed, that needs to be escalated, I have to sign some agreement that I will not pass on the beta firmware, and then they send it over.